Folia Endocrinologica Japonica

The binding of ¹²⁵I-labeled human luteinizing hormone (hLH) to the human luteal tissue of the menstrual cycle was examined. Displacement studies demonstrated that ¹²⁵I-hLH was specifically bound to the human luteal tissue. Specific binding of ¹²⁵I-hLH was demonstrated in all the corpora lutea examined except for two aged corpora lutea at the early proliferative phase of the cycle. The number of binding sites for hLH increased from the early to mid-luteal phase and decreased towards the late luteal phase. However, the apparent dissociation constant in each corpus luteum did not vary throughout the menstrual cycle. Furthermore, the effects of diethylstilbestrol diphosphate (DES) and prostaglandin F2a (PGF_2α) priming on the binding of ¹²⁵I-hLH to the luteal tissue were investigated and the changes in hLH receptors were estimated by Scatchard plot. The binding sites for hLH decreased by DES priming and increased by PGF_2α priming. In contrast, the apparent dissociation constant in each luteal tissue revealed almost the same value. The results of the present investigation suggest that estrogen and prostaglandin might modulate LH receptor in human corpora lutea during the menstrual cycle.

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Binding of ¹²⁵1-labeled rat FSH to a testicular homogenate of Japanese quail cockerels increased progressively with age when the cockerels were reared under long day photoperiods from day of hatch. The binding per unit weight of tissue (density of binding) showed an increase from day 23 to 29. The binding per testes (total binding) rapidly increased from day 23 to 36. Both density and total binding remained low in cockerels reared under short day photoperiods. Injections of testosterone into newly hatched cockerels at 1 mg/day for 3 days increased the density of binding but did not increase the testicular weight. Injections of NIH-FSH-S12 at 16 μg/day for 3 days did not increase the density of binding but in-creased both total binding and testicular weight. Combined administration of FSH and testosterone increased all of the density of binding, the total binding and the testicular weight. The synergistic action of FSH and testosterone was observed in these increases. Hypophysectomy of male adult Japanese quail resulted in a rapid decrease of the total binding. This suggests a decrease in binding per Sertoli cell. Injections of testosterone into hypophysectomized birds at 5 mg/day for 5 days increased the binding per Sertoli cell but did not change the cell size. Injections of NIH-FSH-S12 at 100 μg/day for 5 days increased the binding per Sertoli cell and at the same time induced hypertrophy of Sertoli cells. Combined administration of FSH and testosterone increased all the parameters, showing the presence of synergisim between these hormones. The Scatchard plot analysis of the binding showed that the increase of the binding was due to the change in the number of binding sites but not to the change in the affinity. These results indicated that FSH receptors in the testis are regulated by FSH and testosterone. It is suggested that FSH acting synergistically with testosterone elevates the sensitivity of the testis to FSH itself by increasing FSH receptors. This self-potentiation mechanism seems to enable extremely rapid development of the testis in photostimulated birds and mammals at puberty.

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